feat(core): introduce coreapp api

diff --git a/core/SConscript.firmware b/core/SConscript.firmware
index 618d6d5c..34e16832 100644
--- a/core/SConscript.firmware
+++ b/core/SConscript.firmware
@@ -88,6 +88,9 @@ if PYOPT == '0':
 if DBG_CONSOLE != "":
     FEATURES_WANTED += ["dbg_console"]
 
+if TREZOR_MODEL in ['T3W1']:
+    FEATURES_WANTED += ["app_loading"]
+
 CCFLAGS_MOD = ''
 CPPPATH_MOD = []
 CPPDEFINES_MOD = []
@@ -276,6 +279,9 @@ SOURCE_MOD += [
 if not PRODUCTION:
     SOURCE_MOD += ['embed/rtl/printf.c']
 
+if "app_loading" in FEATURES_WANTED:
+    SOURCE_MOD += ['embed/api/trezor_api_v1_impl.c']
+
 CPPDEFINES_MOD += [
     'TRANSLATIONS',
     'FANCY_FATAL_ERROR',
@@ -485,6 +491,7 @@ env.Replace(
 
 ALLPATHS = [
         '.',
+        'embed/api',
         'embed/rust',
         'embed/projects/firmware',
         'embed/rtl/inc',
diff --git a/core/SConscript.kernel b/core/SConscript.kernel
index f9580f44..812657c4 100644
--- a/core/SConscript.kernel
+++ b/core/SConscript.kernel
@@ -82,6 +82,9 @@ if DBG_CONSOLE != "":
 if not TREZOR_MODEL in ['T3W1', 'D002']:
     FEATURES_WANTED += ["secure_mode"]
 
+if TREZOR_MODEL in ['T3W1']:
+    FEATURES_WANTED += ["app_loading"]
+
 if DISABLE_OPTIGA:
     # TODO use PYOPT instead of PRODUCTION, same as in firmware, blocked on #4253
     if PRODUCTION:
diff --git a/core/SConscript.unix b/core/SConscript.unix
index 3355de86..e17d8cad 100644
--- a/core/SConscript.unix
+++ b/core/SConscript.unix
@@ -56,6 +56,9 @@ if BITCOIN_ONLY == '0':
 if not DISABLE_TROPIC:
     FEATURES_WANTED.append('tropic')
 
+if TREZOR_MODEL in ['T3W1']:
+    FEATURES_WANTED += ["app_loading"]
+
 if not models.has_emulator(TREZOR_MODEL):
     # skip unix build
     env = Environment()
@@ -421,6 +424,10 @@ SOURCE_UNIX = [
     'vendor/micropython/shared/runtime/gchelper_generic.c',
 ]
 
+if "app_loading" in FEATURES_WANTED:
+    SOURCE_UNIX += ['embed/api/trezor_api_v1_impl.c']
+
+
 TRANSLATION_DATA = [
     "translations/en.json",
     "translations/order.json",
diff --git a/core/embed/api/trezor_api.h b/core/embed/api/trezor_api.h
new file mode 100644
index 00000000..fc6ee11d
--- /dev/null
+++ b/core/embed/api/trezor_api.h
@@ -0,0 +1,24 @@
+/*
+ * This file is part of the Trezor project, https://trezor.io/
+ *
+ * Copyright (c) SatoshiLabs
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "trezor_api_v1.h"
+
+typedef void* (*trezor_api_getter_t)(uint32_t version);
diff --git a/core/embed/api/trezor_api_v1.h b/core/embed/api/trezor_api_v1.h
new file mode 100644
index 00000000..208e1094
--- /dev/null
+++ b/core/embed/api/trezor_api_v1.h
@@ -0,0 +1,75 @@
+/*
+ * This file is part of the Trezor project, https://trezor.io/
+ *
+ * Copyright (c) SatoshiLabs
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <sys/sysevent.h>
+#include <sys/system.h>
+#include <sys/systick.h>
+
+#ifdef USE_DBG_CONSOLE
+#include <sys/dbg_console.h>
+#endif
+
+#ifdef USE_IPC
+#include <sys/ipc.h>
+#endif
+
+#ifndef USE_DBG_CONSOLE
+// temporary hack to allow compilation when DBG console is disabled
+ssize_t dbg_console_write(const void* data, size_t data_size);
+#endif
+
+typedef struct {
+  void (*system_exit)(int exitcode);
+
+  void (*system_exit_error)(const char* title, const char* message,
+                            const char* footer);
+
+  void (*system_exit_error_ex)(const char* title, size_t title_len,
+                               const char* message, size_t message_len,
+                               const char* footer, size_t footer_len);
+
+  void (*system_exit_fatal)(const char* message, const char* file, int line);
+
+  void (*system_exit_fatal_ex)(const char* message, size_t message_len,
+                               const char* file, size_t file_len, int line);
+
+  ssize_t (*dbg_console_write)(const void* data, size_t size);
+
+  uint32_t (*systick_ms)(void);
+
+  void (*sysevents_poll)(const sysevents_t* awaited, sysevents_t* signalled,
+                         uint32_t deadline);
+
+  ssize_t (*syshandle_read)(syshandle_t handle, void* buffer,
+                            size_t buffer_size);
+
+  bool (*ipc_register)(systask_id_t remote, void* buffer, size_t size);
+
+  void (*ipc_unregister)(systask_id_t remote);
+
+  bool (*ipc_try_receive)(ipc_message_t* msg);
+
+  void (*ipc_message_free)(ipc_message_t* msg);
+
+  bool (*ipc_send)(systask_id_t remote, uint32_t fn, const void* data,
+                   size_t data_size);
+
+} trezor_api_v1_t;
diff --git a/core/embed/api/trezor_api_v1_impl.c b/core/embed/api/trezor_api_v1_impl.c
new file mode 100644
index 00000000..d90994f2
--- /dev/null
+++ b/core/embed/api/trezor_api_v1_impl.c
@@ -0,0 +1,51 @@
+/*
+ * This file is part of the Trezor project, https://trezor.io/
+ *
+ * Copyright (c) SatoshiLabs
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "trezor_api_v1.h"
+
+#ifndef USE_DBG_CONSOLE
+// temporary hack to allow compilation when DBG console is disabled
+ssize_t dbg_console_write(const void* data, size_t data_size) {
+  return data_size;
+}
+#endif
+
+const trezor_api_v1_t trezor_api_v1 = {
+    .system_exit = system_exit,
+    .system_exit_error = system_exit_error,
+    .system_exit_error_ex = system_exit_error_ex,
+    .system_exit_fatal = system_exit_fatal,
+    .system_exit_fatal_ex = system_exit_fatal_ex,
+    .systick_ms = systick_ms,
+    .sysevents_poll = sysevents_poll,
+    .syshandle_read = syshandle_read,
+    .dbg_console_write = dbg_console_write,
+    .ipc_register = ipc_register,
+    .ipc_unregister = ipc_unregister,
+    .ipc_try_receive = ipc_try_receive,
+    .ipc_message_free = ipc_message_free,
+    .ipc_send = ipc_send,
+};
+
+const void* coreapp_api_get(uint32_t version) {
+  if (version == 1) {
+    return &trezor_api_v1;
+  }
+  return NULL;
+}
diff --git a/core/embed/sys/startup/stm32f4/vectortable.S b/core/embed/sys/startup/stm32f4/vectortable.S
index 31e81760..f996e2e1 100644
--- a/core/embed/sys/startup/stm32f4/vectortable.S
+++ b/core/embed/sys/startup/stm32f4/vectortable.S
@@ -135,12 +135,12 @@ vector_table:
   .word reset_handler
   .word _stack_section_start
   .word _stack_section_size
-  .word 0
-  .word 0
-  .word 0
-  .word 0
-  .word 0
-
+  .word 0 // TLS start
+  .word 0 // TLS size
+  .word 0 // API interface getter
+  .word 0 // SAES unpriv input
+  .word 0 // SAES unpriv output
+  .word 0 // SAES unpriv callback
 #endif
 
   .end
diff --git a/core/embed/sys/startup/stm32u5/vectortable.S b/core/embed/sys/startup/stm32u5/vectortable.S
index 6ab99c43..ccce9c69 100644
--- a/core/embed/sys/startup/stm32u5/vectortable.S
+++ b/core/embed/sys/startup/stm32u5/vectortable.S
@@ -185,6 +185,11 @@ vector_table:
   .word _stack_section_size
   .word _tls_section_start
   .word _tls_section_size
+#ifdef USE_APP_LOADING
+  .word coreapp_api_get
+#else
+  .word 0
+#endif
 #if USE_STORAGE_HWKEY
   .word saes_unpriv_input
   .word saes_unpriv_output
diff --git a/core/embed/sys/task/inc/sys/coreapp.h b/core/embed/sys/task/inc/sys/coreapp.h
index 492ddf10..3667a716 100644
--- a/core/embed/sys/task/inc/sys/coreapp.h
+++ b/core/embed/sys/task/inc/sys/coreapp.h
@@ -37,6 +37,8 @@ typedef struct {
   mpu_area_t stack;
   // TLS area
   mpu_area_t tls;
+  // API interface getter
+  void* api_getter;
   // Unprivileged SAES input buffer
   void* saes_input;
   // Unprivileged SAES output buffer
@@ -72,4 +74,8 @@ mpu_area_t coreapp_get_tls_area(void);
 
 #endif  // TREZOR_EMULATOR
 
+#ifdef USE_APP_LOADING
+void* coreapp_get_api_getter(void);
+#endif
+
 #endif  // KERNEL_MODE
diff --git a/core/embed/sys/task/stm32/coreapp.c b/core/embed/sys/task/stm32/coreapp.c
index 5b2c071b..a6f4f628 100644
--- a/core/embed/sys/task/stm32/coreapp.c
+++ b/core/embed/sys/task/stm32/coreapp.c
@@ -31,6 +31,7 @@
 
 static mpu_area_t coreapp_code_area;
 static mpu_area_t coreapp_tls_area;
+static void* coreapp_api_getter = NULL;
 
 // defined in linker script
 extern uint32_t _kernel_flash_end;
@@ -89,6 +90,7 @@ bool coreapp_init(applet_t* applet, uint32_t cmd, const void* arg,
   // (we will need then later for extension applets)
   coreapp_tls_area = header->tls;
   coreapp_code_area = applet->layout.code1;
+  coreapp_api_getter = header->api_getter;
 
   // Reset the applet task (stack pointer, etc.)
   if (!systask_init(&applet->task, header->stack.start, header->stack.size, 0,
@@ -119,4 +121,6 @@ mpu_area_t coreapp_get_code_area(void) { return coreapp_code_area; }
 
 mpu_area_t coreapp_get_tls_area(void) { return coreapp_tls_area; }
 
+void* coreapp_get_api_getter(void) { return coreapp_api_getter; }
+
 #endif  // KERNEL
diff --git a/core/embed/sys/task/unix/coreapp.c b/core/embed/sys/task/unix/coreapp.c
index b0368e1e..0b8792ff 100644
--- a/core/embed/sys/task/unix/coreapp.c
+++ b/core/embed/sys/task/unix/coreapp.c
@@ -27,6 +27,9 @@
 
 extern int coreapp_emu(int argc, char** argv);
 
+// API getter function implemented in the coreapp
+extern const void* coreapp_api_get(uint32_t version);
+
 bool coreapp_init(applet_t* applet, int argc, char** argv) {
   const applet_layout_t coreapp_layout = {0};
   const applet_privileges_t coreapp_privileges = {0};
@@ -45,4 +48,8 @@ bool coreapp_init(applet_t* applet, int argc, char** argv) {
   return true;
 }
 
+#ifdef USE_APP_LOADING
+void* coreapp_get_api_getter(void) { return (void*)coreapp_api_get; }
+#endif
+
 #endif  // KERNEL